I don’t know if this movie is in black & white or if I only saw it on black & white televisions.
There were 3-4 adults, one of which was a woman. They were somewhere (another planet maybe?) where either vines or giant snakes would come after them, and if they died, they turned to mud and dissolved.
It was in English, and I saw it around 1974 or so.
The Day of the Triffids?
Island of Terror?
“The Navy vs the Night Monsters” (1966)?
https://youtu.be/9fX3dcYw440